A quad cab has four doors where an extended cab may have just
two doors or two full doors and two smaller, reverse doors. A quad
cab is basically a crew cab, though Dodge has a quad cab and a crew
cab. The Dodge crew cab is a bit more spacious on the inside. If
you have people in the back seat of a Dodge, the extended cab will
have the least space for them, then the quad cab and the crew cab
the most.